1. Field of the Invention
The present invention relates to a computer housing, and more particularly, to a computer housing for preventing an electromagnetic radiation leakage.
2. Description of the Prior Art
Generally, various kinds of electronic components have been installed in a computer system, and all these electronic devices emit electromagnetic radiation. Moreover, the electromagnetic radiation will be harmful to the computer users and circumstances. It is therefore desirable for the computer manufacturers to shield circuit components to reduce undesirable electromagnetic interference (EMI) with the use of computer housing shields that reflect or dissipate electromagnetic charges and fields.
Computer chassis is often provided with extra circuit card slots to allow for easy expansion of the computer system through the addition of circuit cards. Briefly speaking, all kinds of peripheral equipments can be connected to the computer system by connecting circuit cards to the main board. Generally speaking, those circuit cards, such as FAX enabling demodulation cards, have to be connected to computer system through extra circuit card slots, namely expansion slots, which is mostly installed on the backplane of the computer housing. Therefore, the circuit cards can be inserted into the expansion slots with printed circuit board (PCB) brackets being covered on the expansion slots to communicate with the computer system.
The expansion slots will not be equipped with circuit cards and covered by printed circuit board brackets when a computer is originally shipped or sold. Unless they are shielded, empty slots allow the introduction of dust or other foreign matters into the computer housing, thereby potentially interfering with the performance and life span of the internal circuitry of the computer. Such unshielded empty expansion slots also allow the leakage of electromagnetic (EM) waves generated by the internal circuitry of the computer. Recently, the Federal Communications Commission has imposed limits on the amounts of EM wave emissions released from devices being sold and transported in and around the United States and, therefore, it is desirable to minimize those emissions.
Generally, the empty expansion slots should be covered by brackets. However, nowadays, along with the higher complexity of the electric circuits inside the computer, the amount of electromagnetic radiation is greatly increasing so that lots of queries are raised toward the shielding function of the brackets. Those queries are mainly aimed at the slight gap between the bracket and the computer housing that may cause a leakage of electromagnetic radiation and make the shielding performance of the bracket deteriorated by external forces.
Please refer to FIG. 1, which is a schematic diagram of a computer housing 10 in the prior art. The computer housing 10 comprises a plurality of expansion slots 12 that permit peripherals to connect to a computer system. The computer housing 10 further comprises a plurality of ribs 18 used to separate adjacent expansion slots 12. Typically, the expansion slots 12 of the computer housing 10 should be covered by a plurality of brackets 14 or PCB brackets 15 as shown in FIG. 1. For the sake of clarity, the PCB bracket 15 shown in FIG. 1 does not include a printed circuit board attached thereto, and only a plurality of support arms 32 of the printed circuit board are shown. The embodiment in the prior art as shown in FIG. 1 discloses two ways to fix the brackets 14 and the PCB brackets 15 onto the expansion slots 12 of the computer housing 10. First, the rib 18 may include a supporting hook 16 at one end to hold a bracket 14 to the expansion slot 12, and typically a plurality of screws (not shown) are used to hold the bracket 14 to the other end of the rib 18. The other method to fix the bracket 14 and the PCB bracket 15 onto the computer housing 10 is to install a plurality of openings 20 at one end of the expansion slot 12, and provide the corresponding end of the brackets 14 with a bending tip 22 that can be inserted into the opening 20 for holding the brackets 14. The design of the openings 20 and the bending tip 22 can improve the fixity of the brackets 14. In addition, the above-mentioned two methods can be combined so that the user can easily and quickly fix the brackets 14 between the adjacent ribs 18 of the computer housing 10 and cover the corresponding expansion slot 12. Although the manner of shielding the expansion slots 12 with brackets 14 and/or PCB brackets 15 by the supporting hook 16, the opening 20, and/or bending tip 22 has been proven to be sufficient to block dust and other debris from entering the computer system, such configuration is still inadequate to sufficiently block EM and RF wave emissions.
The prior art as shown in FIG. 1 cannot significantly reduce the slight gap between the bracket 14 and the computer housing 10 that may cause a leakage of electromagnetic radiation. Especially when an external force is applied so as to cause the deformation of the rib 18 or the brackets 14, the gap between the bracket 14 and the computer housing 10 may be deformed by the external force. In order to provide a tighter contact between the computer housing 10 and the brackets 14 as shown in FIG. 1 for sufficiently reducing the existed gap, the industrial circles adopt the following technique as shown in FIG. 2.
Please refer to FIG. 2, which is a schematic diagram of the computer housing 10 shown in FIG. 1 with a plurality of metallic shielding panels 24 attached thereto. The installation of the plurality of metallic shielding panels 24 on the ribs 18 can reduce the gap between the brackets 14 and the ribs 18. The metallic shielding panels 24 can be replaced by plastic gaskets. These metallic shielding panels or gaskets 24 can definitely reduce the gap between the rib 18 and the brackets 14 to provide a sounder shielding function. However, those externally added matters cause some problems. First, the installation of the metallic shielding panels or gaskets 24 will consume additional labor and cost. Moreover, the metallic shielding panel (gasket) 24 may conflict with the bending tip 22 of the brackets 14 during the assembling and dissembling processes, resulting in an inconvenience. In particular, due to the increasing quantities of the expansion slots 12 that lead to narrower and thinner ribs 18 and brackets 14, the ribs 18 and brackets 14 are more easily deformed by inadequate external force. If the rib 18 and the bracket 14 are bent toward the same direction, the gap is still within tolerance. If the rib 18 and the bracket 14 are bent toward different directions, the gap will be aggravated beyond tolerance, and thus the metallic shielding panels (gasket) 24 will no longer be clamped between the brackets 14 and the ribs 18. Therefore, the prior art can not really provide a solution for the leakage of electromagnetic radiation.
There are many patent documents related to the shielding design of the computer housing for preventing a leakage of electromagnetic radiation as above-mentioned embodiments. U.S. Pat. No. 5,067,041, “Apparatus for reducing electromagnetic radiation from a computer device”, issued to Cooke et al. teaches some specific shielding designs for various components of the whole computer system. U.S. Pat. Nos. 5,463,532 and 5,679,923, issued to Le and Petitpierre et al. suggest some improvements for the metallic shielding panel as shown in FIG. 2 to achieve easy integration and sound shielding.
In summary, the above-mentioned prior arts have a characteristic in common, that is, they ignore the real cause of the deformation by external forces. That is, the gap between the brackets and the ribs will be aggravated by external forces when the rib and the bracket are bent or twisted toward different directions. Besides, all the prior arts need to install extra components, as metallic sheilding panel, gasket, or supporting hook, for fixing the brackets or for reducing the gap, and all these additional components will bring some bad effects such as increasing cost or inconvenient installation.